San Francisco– Figuring out the next game changer in digital marketing is like handicapping a horse race.

Will it be Facebook’s new location-based service that allows people to share their location by “checking in” to a place and letting friends know where they are – much like Foursquare and Gowalla?

Will geo-location services, combined with the popularity of the iPhone and other phones running on the Android operating system, make mobile advertising a reality sooner rather than later? Or can Twitter, which introduced sponsored tweets four months ago, expand its ad offerings in coming months or years?

Will search management platforms and display advertising platforms end up in a fierce competition? Increasing the likelihood of a battle is news that search agencies are partnering with demand-side platforms and exchanges.

In town for ClickZ’s Connected Marketing Week in San Francisco this week, I chatted with dozens of marketers and listened to scores of presentations; marketers didn’t agree on where things are headed, but it sure looks like things are about to get even more exciting and dynamic.

Facebook, Twitter, and the Power to Change Behavior

So what’s behind the success of Facebook, Twitter, and some other social networks?

BJ Fogg, director of Stanford University’s Persuasive Technology Lab, has investigated the psychology of Facebook and sums up the social network’s success to this factor: “Putting ‘hot triggers’ in the path of motivated people.”

Case in point: let’s say you get a message in your e-mail inbox alerting you that you’ve been tagged in a photo on Facebook. Most likely, you will log onto Facebook to view the photo. Next thing you know, you are checking out your friends’ news feeds and photos. And as you continue to troll the social network, you realize that you have frittered away 30 minutes or more.

“Facebook is doing something right. The way that Facebook is triggering our behavior, it’s no accident they are the fast growing [social network],” he said during a keynote address at SES San Francisco. What’s more, Twitter and others are finding success by following a similar recipe.

Fogg said drama playing out among some tech companies – such as Facebook and Zynga – is related to efforts to control these so-called triggers. Why? Companies that control these “hot triggers” will also be able to control behaviors, he said.

He also differentiated between the roles of search and social. People using search have a very different mission than those visiting social networks. “[With social], they are there to be distracted, get off track. With search, it’s opposite. I’m at point A and need to get to point B,” he said.

Fogg discussed factors that motivate people to change their behaviors, from seeking out pleasure versus avoiding pain; following their hopes versus avoiding their fears; and seeking acceptance versus avoiding rejection. Social networks like Facebook and MySpace, which encourage people to comment on other people’s statuses, for instance, feed into peoples’ needs to be liked and accepted, he said.

LinkedIn and eBay, meanwhile, are examples of companies that take “lightweight” approaches to motivating behavior. LinkedIn’s symbol showing how many people you are connected to encourages you to add other people to your network; the feedback system on eBay is simple and straightforward, prompting trust.

“If you motivate too much, it gets ugly. It can backfire; it can feel heavy handed and it won’t work in the long-term,” he said.

As for mobile devices, Fogg predicted that they will be the “number-one platform for persuasion” in 10 to 15 years. “If you want to influence people, it will be more important than the Web, than TV.” But why will it take so long to gain acceptance? “We’re going to see a lot of failure,” he said. “It needs to help people do what they already want to do. Otherwise, it will feel like it’s a device that’s betraying me…In my book, you don’t adopt mobile devices. You marry them.”